As the developments of multi-media, broad band telecommunication systems have been increasingly demanded. It has been in practical use an optical transmission system operating on a frequency over 10 GB/s and demanded a new system operating on a higher frequency. An LN optical modulator is used as a device for modulating an electrical signal (microwave signal) of 10 GB/s or higher to light.
It is necessary to mount such an optical modulator in a package for connecting it to an outer high frequency electric source. As a prior art document disclosing such electrical mounting structure of the optical modulator, it is described a method of directly connecting a connector pin to the modulator without intervening a high frequency intermediate substrate, in FIG. 1 of Japanese Patent No. 3824265B.
According to an optical transmitter using an optical modulator having two or more ports whose electrical lengths are not adjusted, it is problematic to have a skew among the input ports (timing of the signals). It is thus necessary to provide an outer device for adjusting the timing for each channel.
For example, according to Japanese Patent Publication No. 2003-233044A, the modulator chip is connected by means of wire bondings, and a high frequency connector is connected with a solder. Since the timing of the signals among a plurality of input ports are not adjusted within such a device, a variable phase shifter is connected to each channel to adjust the timing among the channels.
According to Japanese Patent Publication No. 2004-185040A, a signal electrode is considerably bent between an interacting part and input port of an optical modulator, so that the skew is adjusted among the input ports. In this case, it is unnecessary to adjust the timing of the high frequency electrical signals with the outer phase shifter.